The present disclosure relates to systems and methods for percutaneous implantation of a heart valve prosthesis. More particularly, it relates to delivery systems and methods for transcatheter implantation of a stented prosthetic heart valve.
Heart valves, such as the mitral, tricuspid, aortic, and pulmonary valves, are sometimes damaged by disease or by aging, resulting in problems with the proper functioning of the valve. Heart valve problems generally take one of two forms: stenosis in which a valve does not open completely or the opening is too small, resulting in restricted blood flow; or insufficiency in which blood leaks backward across a valve when it should be closed.
Heart valve replacement has become a routine surgical procedure for patients suffering from valve regurgitation or stenotic calcification of the leaflets. Conventionally, the vast majority of valve replacements entail full stenotomy in placing the patient on cardiopulmonary bypass. Traditional open surgery inflicts significant patient trauma and discomfort, requires extensive recuperation times, and may result in fife-threatening complications.
To address these concerns, within the last decade, efforts have been made to perform cardiac valve replacements using minimally-invasive techniques. In these methods, laparoscopic instruments are employed to make small openings through the patient's ribs to provide access to the heart. While considerable effort has been devoted to such techniques, widespread acceptance has been limited by the clinician's ability to access only certain regions of the heart using laparoscopic instruments.
Still other efforts have been focused upon percutaneous transcatheter (or transluminal) delivery of replacement cardiac valves to solve the problems presented by traditional open surgery and minimally-invasive surgical methods. In such methods, a valve prosthesis is compacted for delivery in a catheter and then advanced, for example through an opening in the femoral artery and through the descending aorta to the heart, where the prosthesis is then deployed in the valve annulus (e.g., the aortic valve annulus).
Various types and configurations of prosthetic heart valves are used in percutaneous valve procedures to replace diseased natural human heart valves. The actual shape and configuration of any particular prosthetic heart valve is dependent to some extent upon the valve being replaced (i.e., mitral valve, tricuspid valve, aortic valve, or pulmonary valve). In general, prosthetic heart valve designs attempt to replicate the function of the valve being replaced and thus will include valve leaflet-like structures used with either bioprostheses or mechanical heart valve prostheses. If bioprostheses are selected, the replacement valves may include a valved vein segment or pericardial manufactured tissue valve that is mounted in some manner within an expandable stent frame to make a valved stent. In order to prepare such a valve for percutaneous implantation, one type of valved stent can be initially provided in an expanded or uncrimped condition, then crimped or compressed around a balloon portion of a catheter until it is close to the diameter of the catheter. In other percutaneous implantation systems, the stent frame of the valved stent can be made of a self-expanding material. With these systems, the valved stent is crimped down to a desired size and held in that compressed state with a sheath, for example. Retracting the sheath from this valved stent allows the stent to expand to a larger diameter, such as when the valved stent is in a desired position within a patient. With either of these types of percutaneous stent delivery systems, conventional sewing of the prosthetic heart valve to the patient's native tissue is typically not necessary.
It is imperative that the stented heart valve prosthesis be accurately located relative to the native annulus prior to full deployment from the catheter. Successful implantation requires that the transcatheter prosthetic heart valve intimately lodge and seal against the native annulus. A self-expanding transcatheter heart valve must have a high radial force when expanding to properly anchor itself in the anatomy of the heart. If the prosthetic is incorrectly positioned relative to the native annulus, serious complications can result as the deployed device will leak and even may dislodge from the implantation site. Greatly complicating this effort is the fact that once the heart valve prosthesis (e.g., a self-deploying stent) is deployed from the catheter, it is exceedingly difficult to re-collapse or “recapture” the prosthetic with conventional delivery tools (e.g., an outer sheath or catheter). This same concern does not arise in the context of other vascular stents; with these procedures, if the target site was “missed,” another stent is simply deployed to “make-up” the difference. In short, recapturing a deployed or partially deployed stent-based device is unique to transcatheter heart valves.
While imaging technology can be employed as part of the implantation procedure to assist a clinician in better evaluating a location of the transcatheter prosthetic heart valve immediately prior to deployment, in many instances, this evaluation alone is insufficient. Instead, clinicians desire the ability to partially deploy the prosthesis and then evaluate a position relative to the native annulus prior to full deployment. While in theory the “re-capturing” of a partially deployed stented prosthetic heart valve is straight forward, in actual practice, the constraints presented by the implantation site and the stented heart valve itself render the technique exceedingly difficult.
In light of the above, although there have been advances in percutaneous valve replacement techniques and devices, there is a continued desired to provide different delivery systems for delivering and repositioning cardiac replacement valves, and in particular self-expanding stented prosthetic heart valves, to an implantation site in a minimally invasive and percutaneous manner. There is also a continuing desire to be able to provide a more controlled deployment of replacement valves, and to be able to reposition and/or retract the valves once they have been deployed or partially deployed in order to ensure optimal placement of the valves within the patient.